A limited-slip differential (LSD) is a type of differential that allows its two output shafts to rotate at different speeds but limits the maximum difference between the two shafts. Limited-slip differentials are often known by the

generic trademark A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products ...

Positraction, a brand name owned by General Motors. In an automobile, such limited-slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.

Early history

In 1932,

Ferdinand Porsche Ferdinand Porsche (3 September 1875 – 30 January 1951) was an Austrian-German automotive engineer and founder of the Porsche AG. He is best known for creating the first gasoline– electric hybrid vehicle ( Lohner–Porsche), the Vol ...

designed a Grand Prix racing car for the

Auto Union Auto Union AG, was an amalgamation of four German automobile manufacturers, founded in 1932 and established in 1936 in Chemnitz, Saxony. It is the immediate predecessor of Audi as it is known today. As well as acting as an umbrella firm ...

company. The high power of the design caused one of the rear wheels to experience excessive wheel spin at any speed up to . In 1935, Porsche commissioned the engineering firm ZF to design a limited-slip differential to improve performance. The ZF "sliding pins and cams" became available, and one example was the Type B-70 used during the Second World War in the military VWs ( Kübelwagen and Schwimmwagen), although technically this was not a limited-slip differential, but a system composed of two

freewheel Freewheel mechanism In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An ov ...

s, which sent the whole of the engine power to the slower-turning of the two wheels.

Benefits

The ma